This invention relates to insulation for electrical wire or cable.
Wire and cable with chemically-resistant dual-wall insulation comprising a polyolefin inner layer and a fluoropolymer outer layer have been commercially available for over 30 years. Such insulation suffers, from a number of performance shortcomings, including a tendency to wrinkling, crack propagation, and peeling of the outer insulation layer.
It has now been surprisingly discovered, according to the present invention, that improved insulation can be provided by a first layer comprising a selected carbonyl-containing polymer and an adjacent second layer comprising a selected fluoropolymer. These layers can be bonded together by cross-linking to provide insulation having improved performance characteristics in one or more areas such as resistance to abrasion, peeling (especially if one of layers is damaged), blistering (especially if beat is applied), delamination, creasing and wrinkling (especially when the insulation is subject to mechanical stress or exposure to solvents).
Throughout this specification, including the claims, the terms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d before an item mean that there can be a single such item or two or more such items, unless the context makes this impossible (for example, in the first aspect of the invention, the first polymeric componene can comprise a single carbonyl-containing polymer as defined or two or more such polymers; and the second polymeric component can contain a single fluoropolymer or a mixture of two or more fluropolymers); and the term xe2x80x9cconsisting essentially ofxe2x80x9d certain ingredients means that those ingredients are necessarily present and that other ingredients may be present providing that they do not have an adverse effect on the desired properties of the insulation.
In a first aspect, this invention provides an electrical wire or cable having insulation comprising:
(I) a first layer which is composed of a first polymeric composition consisting of a first polymeric component and optionally a first non-polymeric component, the first polymeric component comprising at least 20%, preferably at least 40%, more preferably at least 60% or at least 80%, by weight, based on the weight of the first polymeric component, (or, in some embodiments, based on the weight of the whole composition) of a carbonyl-containing polymer (which may be a homopolymer or copolymer, including terpolymer, and which preferably has a non-aromatic backbone), the carbonyl-containing polymer comprising repeating units derived from a monomer which (i) can be copolymerized with an olefinic monomer and (ii) contains a carboxylic acid ester group, preferably an acrylate or acetate, especially an alkyl acrylate (preferably methyl acrylate, ethyl acrylate, propyl acrylate or butyl acrylate), the units derived from said monomer constituting at least 5%, preferably at least 9%, more preferably at least 15%, for example 15 to 28%, by weight of the carbonyl-containing polymer, and any other repeating units of the carbonyl-containing polymer preferably being derived from an olefinic monomer, preferably ethylene;
(II) a second layer which is in direct contact with the first layer at an interface, and which is composed of a second polymeric composition consisting of a second polymeric component and optionally a second non-polymeric component, the second polymeric component comprising at least 10%, preferably at least 50%, particularly at least 90%, for example substantially 100%, by weight based on the weight of the second composition, of a fluoropolymer, and being free of polymers containing more than 50% by weight, based on the weight of the polymer, of repeating units derived from vinylidene fluoride.
Preferably, the layers (I) and (II), while in contact with each other, have been subjected to conditions which cause cross-linking of polymers at the interface between them, preferably by subjecting the layers to radiation, particularly ionising radiation. The cross-linking is preferably such that at least one of the following conditions is fulfilled
(i) the peel bond strength between the layers, measured by ASTM 81876-95, is at least 3N, preferably more than 5N, e.g. more than 10N
(ii) when a sample of the electrical wire or cable is subjected to steps (a), (b) and (c), there is no delamination of the two layers, step (a) being to slit the insulation axially over a length of 50 mm down to the conductor, step (b) being to wrap the wire around a mandrel whose diameter is twice the diameter of the insulated wire, with the slit on the outside of the wrapped wire, thus exposing the conductor, and step (c) being to unwrap the wire from the mandrel until the wire is straight, and
(iii) the peel bond strength after the crosslinking, measured by ASTM B1876-95, is at least 50% greater, preferably at least 100% greater especially at least 500% or 1000% greater, than the peel bond strength before the crosslinking, measured by ASTM B1876-95.
Throughout this specification, including the claims, the terms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d before an item mean that there can be a single such item or two or more such items, unless the context makes this impossible (for example, in the first aspect of the invention, the first polymeric component can comprise a single carbonyl-containing polymer as defined or two or more such polymers; and the second polymeric component can contain a single fluoropolymer or a mixture of two or more fluoropolymers); and the term xe2x80x9cconsisting essentially ofxe2x80x9d certain ingredients means that those ingredients are necessarily present and that other ingredients may be present providing that they do not have an adverse effect on the desired properties of the insulation.
A second aspect of the invention provides a method of making an insulated wire or cable, the method comprising the steps of
(A) providing an electrical conductor surrounded by
(i) a first layer which is composed of a first polymeric composition as defined in the first aspect of the invention; and
(ii) a second layer which is composed of a second polymeric composition as defined in the first aspect of the invention;
the first and second layers being in direct contact with each other at an interface; and
(B) exposing the layers while in contact with each other to ionising radiation which causes cross-linking of polymers at the interface.